Shift register circuit



June 17, 1952 w. H. BURKHART 2,601,039

SHIFT REGISTER CIRCUIT Filed April 15, 1951 2 SI-IEETS-SHEET 1 FIG.

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:w I I 0 l I I 0 I (J 1561A K131 I AVAVA/V- INVENTOR WILL/AM H. BUR/(HART n n n AGENT June 17, 1952 w BURKHART 2,601,089

SHIFT REGISTER CIRCUIT Filed April 13 1951 2 SHEETS-SHEET 2 F/G.4 A

0p all I lNl/E/V TOR WILL/AM H. BUR/(HART AGENT Patented June 17, 1952 SHIFT REGISTER CIRCUIT William Henry Burkhart, East Orange, N. .l., assignor to Monroe Calculating Machine Company, Orange, N. J., a corporation of Delaware Application April 13, 1951, Serial No. 220,846

8 Claims. 1

This invention. relates to electronic computers and moreparticularly to improved shift register circuits therefor.

In known computers, stable trigger tube pairs are arranged ser'iallyin such manner, that on the occurrence of a shift or advance signal, each trigger pair is set to the state in which the next preceding pair stood prior to the occurrence of said signal. For example, in a shift register, the alternate states of each trigger pair may represent the binary digits zero and one, in which instance, the said advance signal aifects the shifting of each digit to the next succeeding trigger pair of the series.

Heretofore, arrangements of this type have been unsatisfactory in that difficulty washed in obtaining a positive, accurate transfer from a first trigger pair to a second pair when said first pair was itself being shifted to the opposite state under control of a previous trigger pair or an input signal.

The principal object of the invention, therefore, is the provision'of animproved circuit of the type involved which overcomes the disadvantages of the prior art circuits.

According to the invention each trigger pair of a serial array provided with a pair of puller tubes operated selectively to set the trigger differentially, said puller tubes being normally d-is abled but being enabled periodically for short periods of time by an advance or shift signal. Each puller is connected with an output of the next preceding trigger pair through an RC network which provides a time constant that is large with respect to the duration of the advance signal. This arrangement results in that the states of the outputs of the next preceding trigger pair prior to said advance signal are controlling the puller tubes when said signal enables the latter, and positive, accurate shifting is effected.

A modified form of the invention provides a dual puller tube arrangement which requires but a single input line, the two tubes being so interconnected as always to maintain opposite states of conduction.

Other objects and features of the invention will become apparent from the following description when read in the light of the attached drawings of which Fig. 1 is a block diagram which illustrates the principle of the invention.

Fig. 2 is a schematic wiring diagram which illustrates the details of a section of Fig. 1.

Fig. 3 is a schematic wiring diagram similar to Fig. 2' but illustrating a slightly different way of applying control pulses thereto.

Fig. 4 is a curve diagram which illustrates the mode of operation of the means of the invention.

Fig. 5 is a schematic wiring diagram of a modified form of the invention which requires but a single input line.

Referring to Figs. 1 and 2 there is illustrated a series of serially connected stable trigger tube pairs 'IPI, TF2, etc. each controlled by a pair of puller tubes Pl, P2, etc. The trigger tube inputs are connected in the usual fashion to the plates of the puller tubes, so that potential drops at the latter set and reset the triggers. The puller tubes are triodes having their cathodes connected to a sou-roe of positive potential, say +l'0 volts, said positive potential being relieved periodically by negative advanceor shift pulses A of equal potential magnitude. The advance pulses A are of short duration, for example, 5 micro-seconds. The output line I or I of each trigger tube may, for convenience of description, be assumed to be 0 volts or 20 volts depending on the setting of the trigger. Preferably, a zero volt potential on line I indicates that the trigger pair is set to represent binary 1. Each output line I and I is connected with the grid of a puller tube P associated with the next succeeding trigger pair through a resistor Iii and a line all or dI'. A condenser H connects each line di and CH with ground. Each combination of a resistor i0 and a condenser H provides a time constant which affects the rate of reflection of potential changes of line I or I on the associated line di or d1. Preferably the values of these components are chosen to provide a time constant which is large with respect to the duration of the advance pulses A but smaller than the interval of time between successive shift pulses. For example, the values shown in Fig. 2 provide a time constant of 40 micro-seconds. With this time constant, only very small percentage of a potential change of a line I or I' is reflected on the associated line di or dI' during the time span (5 micro-seconds) of an advance pulse A.

The operation of the circuit is as follows.

Assuming that trigger TPI (Fig. 2) has been set to represent binary l by any suitable means, and is reset to represent binary 0 on the occurrence of an advance pulse A, the potential of the output line I of said trigger drops from 0 volts to -20 volts, and the potential of the output line I thereof rises in potential from 20 volts to 0 volts, all as shown at point at in Fig. 4. The potentials of the associated lines dI and all which were the same as those of lines I and 1' prior to the advance pulse, however, do not immediately follow the excursions of the latter but rather follow the characteristic exponential paths indicated in Fig. 4. This results in that only very small potential changes take place on lines (i1 and d1 during the time span of the advance pulse A. On the occurrence of the advance pulse, the potentials of the cathodes of the puller tubes P2 are reduced to volts and the tube associated with line (H which is at 0 volt potential, conducts. The puller tube P2 associated with line all which is at -20 volts, remains cut off. It will readily be seen that the conducting and non-conducting states of the puller tubes are not affected by the small changes in the potentials of lines all and 011' during the time span of the advance pulse.

The conduction of the puller tube associated with line dI lowers the potential of the plate thereof and trigger pair TP2 is set to represent a binary digit 1.

It will be seen, therefore, that there has been provided a circuit for positively shifting the setting of a serially connected trigger pair to the next succeeding trigger pair while the setting of the first said trigger pair is being changed.

Referring now to Fig. 3 there is illustrated a slightly different arrangement from that shown I in Figs. 1 and 2. Here the cathodes of the puller tube pairs are connected to a source of steady positive potential which may conveniently be volts and pulses A which may rise volts from a -20 volt level, are applied periodically to the condenser ll of each RC network H), II.

The operation is as follows.

Assuming that line dI is at 0 volts and line (11' is at -20 volts, both puller tubes are out 01f. The occurrence of an A pulse, however, raises the potential of line (11 toward +20 volts. When this line reaches +10 volts, the associated puller conducts and the potential of its plate drops, setting the associated trigger pair. Line d1 which has a potential of -20 volts is raised to potentials of said lines I and I due to change in the setting of a previous trigger not afiecting the operation of the puller tubes.

In some instances, only one input line I may be provided for each puller tube pair. This is illustrated in Fig. 5 wherein the puller tubes are shown as pentodes having their cathodes grounded and their suppressor grids commonly connected with a source of pulses A which rise 20 volts from a -20 volt potential. One puller tube has its control grid connected by a line dI and an RC network I0, II, with the input line I. The control grid of the other tube is connected to the center point of a voltage divider which extends between sources of negative and positive potentials, in the present instance, and 100 volts. The positive leg of this voltage divider is sectioned as shown and th screen grid of the other puller tube is connected thereto.

The arrangement is such, that if the puller tube associated with line (11 is conducting, the connection between its screen grid and the control grid of the other puller tube lowers the potential of said control grid and cuts off the latter tube. When the former tube is cut off the control grid of the latter tube is at 0 volt potential and said latter tube may conduct. Normally, both tubes are cut off by the -20 volts which are impressed on their suppressor grids. Pulses A, however, remove this cutoff factor, leaving the tubes under control of the potential of line dI. If line (11 is at the low potential of -20 volts, the puller tube associated therewith remains out off and through the connection between its screen grid and the control grid of the other tube, said other tube conducts. If line 011 is at the high potential of 0 volts, the tube associated therewith conducts. Conduction of either tube sets the associated trigger pair the same as described above. Again, it is the potential of line I before the occurrence of the A pulse which controls the operation of the puller tubes, 2. change in the potential of said line that occurs coincidentally with said pulse, not affecting the operation.

In the just described pentode arrangement only one output of a trigger pair is utilized; however, both outputs are shown as they may be utilized to operate triode pullers as described above or pentode pullers not interconnected for alternative conduction.

It is to be understood that the potential levels and the values of the several circuit components utilized in describing and illustrating the invention are only by Way of example and that changes therein to fit individual requirements do not constitute departures from the inventive concept.

While there are above described but a limited number of embodiments of the invention, it is possible to produce still other embodiments without departure from the inventive concept above disclosed, and it is, therefore, desired that only such limitations shall be imposed on the appended claims as are stated therein, or required by the prior art.

I claim:

1. In a circuit of the class described, the combination of a plurality of serially connected trigger tube pairs, a puller tube pair for each trigger pair to set and reset the latter, means normally maintaining said pullers cut off but permitting conduction periodically for short intervals, connecting means between each puller pair and the preceding trigger pair to effect conduction of one puller and maintain the cut-off state of the other during said short intervals in accordance with the setting of said preceding trigger pair, and a time constant network in each connecting means to suppress the effect on the pullers of a change in the setting of the said preceding trigger during a said interval.

2. In a circuit of the class described, the com bination of a plurality of serially connected trigger tube pairs, a puller tube pair for each trigger pair to set and reset the latter, means normally maintaining said pullers cut oii but permitting conduction periodically for short intervals, and an RC network between the outputs of each trigger pair and the inputs of the next succeeding puller pair, each RC network providing a time constant which is large with respect to said short intervals.

3. In a circuit of the class described, the combination of a plurality of serially connected trigger tube pairs, a puller tube pair for each trigger pair to set and reset the latter, means normally maintaining said pullers out off but permitting conduction periodically for short intervals, said means being applied to the cathodes of the pullers, and an RC network between the outputs of each trigger pair and the inputs of the next succeeding puller pair, each RC network providing a time constant which is large with respect to said short intervals.

4. In a circuit of the class described, the combination of a plurality of serially connected trigger tube pairs, a puller tube pair for each trigger pair to set and reset the latter, means normally maintaining said pullers cut off but permitting conduction periodically for short intervals, and an RC network between the outputs of each trigger pair and the inputs of the next succeeding puller pair, each RC network providing a time constant which is large with respect to said short intervals, said means being applied to the condensers of said RC networks.

5. In a circuit of the class described, the combination of a plurality of serially connected trigger tube pairs, a puller tube pair for each trigger pair to set and reset the latter, means normally maintaining said pullers cut off but permitting conduction periodically for short intervals, the inputs of said pullers being connected to the outputs of the next preceding trigger pair, one puller (of each pair) being made conductive at each said interval in accordance with the setting of the preceding trigger pair and setting its associated trigger pair to the state of the former, and a time constant network in the input of each puller to suppress the efiect of a change in the state of the preceding trigger pair during a said interval.

6. In a circuit of the class described, the combination of a plurality of serially connected trigger tube pairs, a pair of pentode puller tubes for each trigger pair, to set and reset the latter, means affecting the suppressor grids of the puller tubes to maintain the latter cut off, said means allowing conduction periodically for short intervals, and an RC network connecting the control grid of one puller of each pair with an output of the next preceding trigger pair and having a time constant which is large compared with a said interval, the control grid of the other 7. In a circuit of the class described, the combination of a plurality of serially connected trigger tube pairs, a pair of pentode puller tubes for each trigger pair to set and reset the latter, means affecting the suppressor grids of the pullers to maintain the latter out ch, said means permitting conduction periodically for short intervals, one output of the preceding trigger pair being connected to the control grid of one tube of each puller pair, to cut oif or allow conduction of said tube in accordance with the setting of said preceding trigger, and a time constant network in said control grid connection to suppress changes in the potential thereof during a said interval due to a change in the state of said preceding trigger pair, the control grid of the other puller of the pair being connected to the screen grid of the first tube to cut off the said other tube when the first tube is conducting and allow conduction when said first tube is cut ofi.

8. In a circuit of the class described, the combination of a plurality of serially connected trigstate of said preceding trigger, and a time conpuller of the pair being connected to the screen "j grid of the first tube to cut oif the said other tube when the first tube is conducting and allow conduction when said first tube is cut oil.

stant network in said connection to suppress the effect on said first tube of changes in the state of said preceding trigger during a said interval.

WILLIAM HENRY BURKHART.

No references cited. 

